Explanation:C₄ photosynthesis is a specialized type of photosynthesis found in some plants, which allows them to better utilize CO₂ and minimize photorespiration. In C₄ plants, the primary CO₂ fixation occurs in the mesophyll cells, where phosphoenolpyruvate (PEP) carboxylase enzyme fixes CO₂ and forms a 4-carbon acid.The C₄ acids formed in the mesophyll cells during C₄ photosynthesis are:- Oxaloacetate (OAA): The initial product formed when CO₂ is fixed to PEP by PEP carboxylase.- Malic acid: Oxaloacetate is reduced to malate in the presence of NADPH, forming malic acid.- Aspartic acid: Oxaloacetate can also be transaminated with glutamate to form aspartate and α-ketoglutarate.These C₄ acids are then transported to the bundle sheath cells, where they release CO₂ to be fixed again by rubisco in the Calvin cycle. This process helps C₄ plants to maintain higher levels of CO₂ in the bundle sheath cells, thereby reducing the rate of photorespiration and increasing their overall photosynthetic efficiency.So, the correct answer is A: OAA or malic acid or aspartic acid.

Answer:

C4 acid, also known as C4 metabolism or C4 pathway, is a type of photosynthetic pathway found in certain plants. In C4 plants, such as corn, sugarcane, and sorghum, C4 acid is formed in the mesophyll cells of the leaf during photosynthesis. The correct answer is option 'A', which includes OAA (oxaloacetic acid) or malic acid or aspartic acid.

Explanation:

1. C4 Plants and C4 Pathway:
C4 plants have evolved a specialized mechanism to enhance photosynthetic efficiency in hot and dry environments. These plants have a unique anatomical and biochemical adaptation called the C4 pathway. The C4 pathway involves the separation of initial carbon fixation and the Calvin cycle into different cells.

2. Mesophyll Cells:
In C4 plants, the C4 acid is formed in the mesophyll cells of the leaf. Mesophyll cells are located between the upper and lower epidermis of the leaf and are responsible for photosynthesis. These cells contain specialized chloroplasts and are the site of initial carbon fixation in the C4 pathway.

3. C4 Acid Formation:
During photosynthesis in C4 plants, carbon dioxide (CO2) is initially fixed into a four-carbon compound, known as C4 acid, in the mesophyll cells. This initial carbon fixation occurs through the enzyme PEP carboxylase, which has a higher affinity for CO2 than the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) found in C3 plants.

4. Types of C4 Acids:
The most commonly formed C4 acids in the mesophyll cells of C4 plants are oxaloacetic acid (OAA), malic acid, and aspartic acid. These C4 acids are then transported to bundle sheath cells, where they are decarboxylated to release CO2, which enters the Calvin cycle. This spatial separation between mesophyll and bundle sheath cells allows for efficient CO2 concentration and reduction in photorespiration.

Conclusion:
In conclusion, C4 acid, formed in the mesophyll cells of C4 plants during photosynthesis, includes OAA, malic acid, or aspartic acid. These C4 acids play a crucial role in the C4 pathway by facilitating efficient carbon fixation and minimizing photorespiration in hot and dry environments.